The present invention relates to optical heads. In particular, the present invention relates to flying optical heads.
Optical data storage systems access data by focusing a laser beam or other light source onto a data surface of a medium and analyzing the light reflected from or transmitted through the medium. In general, data is stored in optical storage systems in the form of marks carried on the surface of the medium which are detected using a reflected laser light.
Compact discs, which are widely used to store computer programs, music and video, are one type of optical data storage system. Typically, compact discs are permanently recorded during manufacture by etching the surface of the compact disc. Another type of optical system is a write once read many (WORM) system in which a user may permanently write information onto a blank disc. Other types of systems are erasable, such as phase change and magneto-optic (M-O) systems. Phase change systems detect data by sensing a change in reflectivity. M-O systems read data by measuring the rotation of the incident light polarization due to the magnetic state of the storage medium.
The above systems require a beam of light to be focused on to a data surface of a disc. Storage density is determined not only by the size of the markings on the data surface, but also by the size of the beam focused on the surface (i.e., resolution). In general, the optics used to focus the beam on the surface can be divided into two groups: those with flying heads and those without flying heads. In those systems that do not use a flying head, a portion of the optics system typically moves radially over the disc to follow tracks on the disc. The moving portion of the optics is supported by a physical structure that extends over the disc. In systems with flying heads, the optics within the head are actually supported by a thin layer of fluid, typically air, that rotates with the disc. By flying on this thin layer of fluid, the optics of the head are positioned extremely close to the surface.
In both systems an objective lens is used to focus the light into a spot on the disc. In a system with a flying head, the objective lens is used in conjunction with a solid-immersion-lens or SIL. The objective lens focuses the beam into the SIL and the SIL reduces the beam spot size by virtue of wavelength reduction which occurs when light passes through optically dense media. Because it is on a flying head, the SIL is positioned very close to the data surface so that light from the SIL couples to the disc surface via evanescent waves.
In both optical systems, as light passes through the objective lens a portion of the light forms fringe fields around the perimeter of the otherwise focused beam. In systems where the objective lens and SIL do not fly over the medium, such as most compact discs, the objective lens is large enough that these fringe fields can be eliminated by coating the outer perimeter of the objective lens with a material that reflects or absorbs light. Alternatively, a separate piece may be inserted above the objective lens to block this extraneous light.
The coating method described above cannot be used with flying optical heads because the objective lens used in flying heads is too small and its hemispherical shape makes it difficult to properly align a mask for depositing material on the lens. Similarly, a separate piece cannot be added to the flying head to block the extraneous light because such a piece would add too much weight to the head.
An optical head for performing optical data operations relative to a medium includes a slider body and at least one lens. Positioned between the slider body and the lens is an aperture stop for blocking the transmittance of light. The aperture stop includes an opaque layer that circumscribes a transparent region.
In preferred embodiments, the aperture stop is deposited directly on the slider body through photolithography methods. The clear slider body allows the aperture stop to be aligned with a feature formed on the opposite side of the slider body.